Molecular basis of differential sensitivity to MeJA in floret opening between indica and japonica rice

Methyl jasmonate (MeJA) accelerated floret opening in rice, crucial for addressing inconsistent floret opening in hybrid seed production of indica × japonica hybrids. However, indica and japonica rice exhibited notable differences in their sensitivity to MeJA's impact on floret opening, with indica responding faster. To clarify the molecular basis of MeJA-induced floret opening sensitivity differences between indica and japonica rice, after 1 h of MeJA spraying, transcriptomes and endogenous floret opening regulators were compared between indica and japonica rice, with histology differences observed. The results showed that MeJA quickly activated plant hormones in indica and japonica rice, but JAZ genes in JA signalling pathway upregulation were greater in indica rice. Alpha-linolenic acid, starch and sucrose metabolism pathways responded faster in indica rice. MeJA boosted endogenous JA synthesis more in indica rice, which had 5-6 middle-layer cells, more than japonica's 3-4 layers, resulting in thicker glumes. The metabolic pathways regulating floret opening, including plant hormone signal transduction, alpha-linolenic acid and starch and sucrose metabolism, along with endogenous JA and soluble sugars, could respond to exogenous MeJA. However, the more intense and rapid responses of these regulatory pathways and endogenous substances to MeJA in indica, resulted in the difference in sensitivity to MeJA between indica and japonica rice.